Testing the Mid-Holocene Relative Sea-Level Highstand Hypothesis in North Wales, United Kingdom

Accurate Holocene relative sea-level curves are vital for modelling future sea-level changes, particularly in regions where relative sea-level changes are dominated by isostatically induced vertical land movements. In North Wales, various glacial isostatic adjustment (GIA) models predict a mid-Holocene relative sea-level highstand between 4 and 6 ka, which is unsubstantiated by any geological sea-level data but affects the ability of geophysical models to model accurately past and future sea levels. Here, we use a newly developed foraminifera-based sea-level transfer function to produce a 3300-year-long late-Holocene relative sea-level reconstruction from a salt marsh in the Malltraeth estuary on the south Anglesey coast in North Wales. This is the longest continuous late-Holocene relative sea-level reconstruction in Northwest Europe. We combine this record with two new late-Holocene sea-level index points (SLIPs) obtained from a freshwater marsh at Rhoscolyn, Anglesey, and with previously published regional SLIPs, to produce a relative sea-level record for North Wales that spans from ca. 13,000 BP to the present. This record leaves no room for a mid-Holocene relative sea-level highstand in the region. We conclude that GIA models that include a mid-Holocene sea-level highstand for North Wales need revision before they are used in the modelling of past and future relative sea-level changes around the British Isles

Sedimentary records of coastal storm surges: Evidence of the 1953 North Sea event

The expression of storm events in the geological record is poorly understood; therefore, stratigraphic investigations of known events are needed. The 1953 North Sea storm surge was the largest natural disaster for countries bordering the southern North Sea during the twentieth century. We characterize the spatial distribution of a sand deposit from the 1953 storm surge in a salt marsh at Holkham, Norfolk (UK). Radionuclide measurements, core scanning X-ray fluorescence (Itrax), and particle size analyses, were used to date and characterise the deposit. The deposit occurs at the onset of detectable 137Cs - coeval with the first testing of nuclear weapons in the early 1950s. The sand layer is derived from material eroded from beach and dunes on the seaward side of the salt marsh. After the depositional event, accumulation of finer-grained silt and clay materials resumed. This work has important implications for understanding the responses of salt marshes to powerful storms and provides a near-modern analogue of storm surge events for calibration of extreme wave events in the geological record